Fruit flies live on every continent of the world except Antarctica, with suitable habitat limited only by temperature and the availability of water. Their common name derives from their habit of laying their eggs on fruit. The larvae eat the fruit when they hatch and become sexually mature within a week. Scientists use fruit flies extensively in genetic research because of their brief life spans and prolific reproduction.
Male fruit flies rub their wings together to make a trilling courtship "song" intended to attract mates. Female fruit flies do become interested and excited by this song, and scientists were interested in what changes occur at the genetic level when animals are stimulated to reproduce. Playing recordings of the sound for female fruit flies not only activated general sensory genes, but also genes associated with the insects' immune systems. Female insects often are damaged physically by the mating process, and can acquire an infection. Scientists speculate female fruit flies have adapted this immune system boost in activity to prepare for the trauma of mating.
Protect and Defend
The activation of females' immune systems in preparation for mating makes sense in light of another discovery that fruit flies' immune systems provide long-term protection from infections. Fruit flies only have innate immunity, which scientists previously believed did not provide long-term protection from infections because it had no memory of earlier infection. Immunity memory normally is retained within an adaptive immunity system, which isn't present in fruit flies. However, research demonstrated fruit flies' immune systems did retain memory of prior infections and how to cope with them. Scientists believe understanding this adaptation could provide new methods of treatment for individuals with compromised immune systems.
Fruit flies' immunity adapts in bacterial as well as genetic ways in response to infections. Fruit flies are susceptible to a common parasite that renders its host sterile. However, a bacteria known as Spiroplasma defeats this parasite and keeps infected fruit flies from losing their reproductive capability. In the early 1980s, this bacteria was present in only 10 percent of eastern fruit flies in North America. By 2010, more than 80 percent of the same populations had become infected with the bacteria, and it was spreading west to protect other populations against the parasite. Scientists don't know precisely how the bacteria kills the parasite, or how fruit flies know to ingest the bacteria.
It's Getting Hot in Here
There's a limit to fruit flies' adaptive capabilities, however. These insects require warm temperatures and humidity to survive -- but not too warm. While a few species have adapted to hotter, tropical environments, most have not. Analysis of fruit flies' resistance to global climate change indicates they lack the ability to adapt to further increases in temperature. Those in tropical areas often have already reached their maximum threshold, and a global temperature increase of even 1 degree could mean the extinction of these species.